solve for r, then find the area of the circular plot of land in square feet ... you'll have to convert that to acres.

for an area 4 times greater, r would have to be doubled, right? why?

Yes I made a sketch and got r=764.98..so then I would need to use the surface area of a cone formula? I get 3676972.5 when I used the formula for that. So if I am converting correctly I get 84.4 acres. Is this correct?